It is true that the coincidence was embarrassing: Mitt Romney, being pressured by fellow Republicans to publish his tax returns, did so on the same day that Barack Obama gave his State of the Union address, in which he attacked precisely the alleged injustice that those tax returns exemplified. The very rich pay federal taxes at a lower rate than most of the middle class.

But we knew that, surely? We have been reminded of this time and again, most notably by Warren Buffett, who made a point of saying that it was wrong that he, Buffett, should pay tax at a lower rate than his secretary. Indeed, President Obama had already taken up this point, with Buffett's permission, in a big way, formulating a Buffett Rule.

In his keynote speech this week, Obama had planned to make his understanding of the Buffett Rule clear: the richest one per cent should pay, in federal taxes, not less than 30 per cent. To dramatise the message, Buffett's secretary herself, Debbie Bosanek, was invited to sit in on the event, in a place of honour next to the President's wife.

All this must have been discussed and evaluated well in advance of the event, and well before Romney's published returns revealed, hours before the State of the Union speech, that last year he paid just under 14 per cent on an income of $27 million.

Yes, the coincidence was embarrassing. But was it more embarrassing than usual? I often find myself embarrassed for the Republicans, never more so than when they repeat their hysterical refusal to allow anything other than tax cuts as an answer to society's or the economy's needs. But then I often find myself embarrassed for the Democrats too. Really, political life here can pass in a vortex of embarrassment.

So who is this tweeting? "Romney's tax returns might kill his chances. See Republican establishment panic now." Rupert Murdoch: why should Murdoch feel that an orderly tax return, showing a prudent use of available loopholes, and resulting in a satisfactorily low overall federal tax bill, should kill a rich man's chances of running for the White House? And why the alleged establishment panic?

Let us exclude for a moment the real possibility that Murdoch and his own tax advisers took one look at Romney's published figures and saw, as others have, that there is more to come, and that if you were able to look at the candidate's previous years' returns you would find him paying even less, and making more controversial use of, for example, his Swiss bank account, or his Cayman Islands portfolio, or some "deferred interest" boondoggle.

On the presently available evidence, why is it wrong that a man whose income comes from investments rather than his salary (he has no salary) should pay a tax which reflects the well-known fact that income from investments is taxed at a different rate from wages or salary? Maybe the embarrassment comes from no more than this: we can be told these things but we don't quite take them in until we see an example as extreme as this.

Perhaps most people think of a tax return as including a modest mix of salary and investment income, in which the lower rate of tax on investment income seems like nothing more than a welcome break. They aren't expecting to encounter such an enormous welcome break as Governor Romney enjoys every year.

Then there is the feeling reported among private equity firms, who were expecting Romney, being one of them, to be an articulate spokesman for their interests, that he has not only failed to stand up for himself - he has failed them as well. He failed private equity, the reasoning goes, by not being prepared for the attack on his business record when it came, by not volunteering his tax returns until put under pressure, and by insufficient staunchness thereafter.

Beyond this, though, one cannot help feeling that a basic point of doctrine is vulnerable, and that those who propound it know very well that it is vulnerable. The doctrine goes like this: the most important thing for the nation is that the rich grow richer, and that they do so fast. Only if the rich grow richer will all be well.

In this sense, Republican ideology reminds me of the story of Moses and the Promised Land, but with the roles reversed. God causes Moses to lead the people of Israel up Mount Nebo, from where they see the Promised Land. Then he explains that Moses and a few of his cronies will reach the Promised Land but that the people of Israel will never make it. They will have to make do with dying on Mount Nebo.

As long as a kind of deference and altruism prevails among American voters they will be prepared to take pleasure in the thought that Mitt Romney and the few like him will have all the fun in the Promised Land. But the moment they start to question the rigged tax system, the jig is up.

Romney was prepared to defend his business record and philosophy against all Democratic comers. He overlooked the possibility that the attack would come from Newt Gingrich - a man who doesn't really seem to care whether what he says makes sense, so long as it comes over well in the first instance.

On this analysis, Romney's chief mistake so far was to have angered Gingrich with an attack that was too well funded to be, well, fair. He is being paid back now, and has a real fight in Florida. But not perhaps a desperate fight. Panic, at least, is premature.